/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.channel.embedded;
  
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.DefaultChannelPromise;
  import io.netty.channel.EventLoop;
  import io.netty.channel.EventLoopGroup;
  import io.netty.util.concurrent.AbstractScheduledEventExecutor;
  import io.netty.util.concurrent.Future;
  import io.netty.util.internal.ObjectUtil;
  
  import java.util.ArrayDeque;
  import java.util.Queue;
  import java.util.concurrent.TimeUnit;
  
  final class EmbeddedEventLoop extends AbstractScheduledEventExecutor implements EventLoop {
      /**
       * When time is not {@link #timeFrozen frozen}, the base time to subtract from {@link System#nanoTime()}. When time
       * is frozen, this variable is unused.
       *
       * Initialized to {@link #initialNanoTime()} so that until one of the time mutator methods is called,
       * {@link #getCurrentTimeNanos()} matches the default behavior.
       */
      private long startTime = initialNanoTime();
      /**
       * When time is frozen, the timestamp returned by {@link #getCurrentTimeNanos()}. When unfrozen, this is unused.
       */
      private long frozenTimestamp;
      /**
       * Whether time is currently frozen.
       */
      private boolean timeFrozen;
  
      private final Queue<Runnable> tasks = new ArrayDeque<Runnable>(2);
  
      @Override
      public EventLoopGroup parent() {
          return (EventLoopGroup) super.parent();
      }
  
      @Override
      public EventLoop next() {
          return (EventLoop) super.next();
      }
  
      @Override
      public void execute(Runnable command) {
          tasks.add(ObjectUtil.checkNotNull(command, "command"));
      }
  
      void runTasks() {
          for (;;) {
              Runnable task = tasks.poll();
              if (task == null) {
                  break;
              }
  
              task.run();
          }
      }
  
      long runScheduledTasks() {
          long time = getCurrentTimeNanos();
          for (;;) {
              Runnable task = pollScheduledTask(time);
              if (task == null) {
                  return nextScheduledTaskNano();
              }
  
              task.run();
          }
      }
  
      long nextScheduledTask() {
          return nextScheduledTaskNano();
      }
  
      @Override
      protected long getCurrentTimeNanos() {
          if (timeFrozen) {
              return frozenTimestamp;
          }
          return System.nanoTime() - startTime;
     }
 
     void advanceTimeBy(long nanos) {
         if (timeFrozen) {
             frozenTimestamp += nanos;
         } else {
             // startTime is subtracted from nanoTime, so increasing the startTime will advance getCurrentTimeNanos
             startTime -= nanos;
         }
     }
 
     void freezeTime() {
         if (!timeFrozen) {
             frozenTimestamp = getCurrentTimeNanos();
             timeFrozen = true;
         }
     }
 
     void unfreezeTime() {
         if (timeFrozen) {
             // we want getCurrentTimeNanos to continue right where frozenTimestamp left off:
             // getCurrentTimeNanos = nanoTime - startTime = frozenTimestamp
             // then solve for startTime
             startTime = System.nanoTime() - frozenTimestamp;
             timeFrozen = false;
         }
     }
 
     @Override
     protected void cancelScheduledTasks() {
         super.cancelScheduledTasks();
     }
 
     @Override
     public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
         throw new UnsupportedOperationException();
     }
 
     @Override
     public Future<?> terminationFuture() {
         throw new UnsupportedOperationException();
     }
 
     @Override
     @Deprecated
     public void shutdown() {
         throw new UnsupportedOperationException();
     }
 
     @Override
     public boolean isShuttingDown() {
         return false;
     }
 
     @Override
     public boolean isShutdown() {
         return false;
     }
 
     @Override
     public boolean isTerminated() {
         return false;
     }
 
     @Override
     public boolean awaitTermination(long timeout, TimeUnit unit) {
         return false;
     }
 
     @Override
     public ChannelFuture register(Channel channel) {
         return register(new DefaultChannelPromise(channel, this));
     }
 
     @Override
     public ChannelFuture register(ChannelPromise promise) {
         ObjectUtil.checkNotNull(promise, "promise");
         promise.channel().unsafe().register(this, promise);
         return promise;
     }
 
     @Deprecated
     @Override
     public ChannelFuture register(Channel channel, ChannelPromise promise) {
         channel.unsafe().register(this, promise);
         return promise;
     }
 
     @Override
     public boolean inEventLoop() {
         return true;
     }
 
     @Override
     public boolean inEventLoop(Thread thread) {
         return true;
     }
 }